It is conventional in automotive air conditioning systems to use a control valve to regulate the flow of refrigerant into the evaporator. The control valve throttles flow of the refrigerant liquid passing from the condenser into the evaporator to thereby reduce the pressure of the refrigerant entering the evaporator and provide efficient operation of the system.
In U.S. Pat. No. 5,479,786, assigned to the assignee of the present invention, which is incorporated herein by this reference, a flow regulating device is disclosed and claimed which comprises a member sealingly received in a conduit of an air conditioning system. Passageways are formed in the member having an inlet on one side and an outlet on the other side of the seal. A temperature responsive thermostatic metal element has one end fixedly mounted to the member and an opposite end movable to open and close at least a portion of the inlet of a passageway in dependence upon the temperature of the thermostatic metal element. In certain ones of the several embodiments disclosed in the patent, the thermostatic metal element is formed into a helix with a movable end coupled to a sleeve rotatably mounted on the member and adapted to rotate in dependence upon the temperature of the thermostatic metal element to increase the amount of restriction for blocking the inlet of a passageway as the temperature of the refrigerant, and concomitantly the thermostatic metal element, increases.
Flow valves made in accordance with the teachings of the above patent are very effective in varying flow restriction in response to refrigerant temperature exiting the condenser wherein more restriction of the flow is provided at high temperatures occasioned by idling or stop and go driving in especially high environmental temperatures and less restriction of the flow is provided at low or road temperatures and with variable flow provided in between the two extremes to obtain improved cooling efficiency. However, under especially heavy load conditions, full restriction can result in excessive pressure of the compressor causing disengagement of the compressor clutch so that the compressor is no longer driven by the engine. This in turn results in substantial loss of cooling efficiency and a general increase in cabin temperature of the vehicle.